This application claims the priority of German Patent Document 199 53 495.0, filed November 6, 1999, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a drive unit for a motor vehicle with an internal combustion engine, a transmission having an output shaft for driving vehicle wheels and an electric drive motor which is selectively engaged to drive the vehicle wheels.
German Patent Document DE 27 32 974 A1 already discloses a drive unit, where a utility vehicle, which is explained with reference to a bus as an example, is equipped with an electric motor, with which the vehicle is driven in normal driving mode. Furthermore, this vehicle is equipped with an internal combustion engine, with which the vehicle can be driven alternatively or additionally to the electric motor. If no supply of electric energy is guaranteed, because, for example, the accumulators in the vehicle are empty or because no overhead line is provided over one segment of the driving distance, the vehicle can be driven then solely with an internal combustion engine. If the vehicle is supposed to be moved up an incline, the vehicle can be driven by both the electric motor and the internal combustion engine, in order to increase the available power. It is stated that the internal combustion engine is dimensioned in such a manner in proportion to the electric motor that the maximum power output of the internal combustion engine is approximately ⅓ to ⅕ of the maximum power output of the electric motor. Owing to this ratio the vehicle is driven with the electric motor in normal driving mode. In the construction of the drive unit, the electric motor forms a part of the cardan shaft of the drive unit and thus also a part of the output shaft of the transmission. Between the internal combustion engine and the transmission, on the one hand, as well as that part of the power train that comprises the electric motor up to the drivable wheels of the vehicle there is a coupling device, with which the internal combustion engine and the transmission can be separated from the rest of the power train.
Starting from this state of the art, the present invention is concerned with the problem of expanding applications of an electric drive for vehicles.
The invention solves this problem by providing a drive unit, according to which the electric engine is dimensioned in such a manner in its outer dimensions that in a motor vehicle, which is designed primarily to be driven by an internal combustion engine, said electric engine can replace a part of the transmission output shaft.
Thus, it is possible in an advantageous manner to provide the hybrid drive as a special accessory for a motor vehicle without the need for extensive design differences in the installation of a hybrid drive as compared to the installation of a single drive by means of the internal combustion engine and without all of the additional drawbacks, such as increased production costs and the more extensive logistics. Thus, a motor vehicle with a purely conventional drive can be equipped in a simple manner orxe2x80x94as additional accessoryxe2x80x94with a hybrid drive.
Owing to the given length of the output shaft of the transmission, such a drive unit turns out to be especially advantageous in a vehicle whose rear wheels can be driven and where the internal combustion engine is housed in the front.
When the electric motor is dimensioned correspondingly, the underfloor of the motor vehicle does not have to be modified, if the dimensions of the electric motor are not at least significantly greater than those of that segment of the output shaft of the transmission that the electric motor replaces.
In the design of the drive unit of certain preferred embodiments of the invention, the electric motor is mounted on its own shaft. Thus, the flexibility of the design of the drive unit is further increased so that the design of the drive unit with a hybrid drive as special accessory can be implemented comparatively inexpensively in that the electric motor is self-bearing. There is no additional design cost to provide bearing holding points for the electric motor when it is supposed to be installed.
In the design according to certain preferred embodiments of the invention, the electric engine is mounted at least somewhat springy at the transmission case. Thus, the electric motor can be supported so as to be carried. At the same time the springy mounting can absorb the oscillations of the power train in that the cardan shaft intermediate bearing is relieved.
In the design of the drive unit, according to certain preferred embodiments of the invention, the torque bracing element of the electric engine is a component of a mechanical connection of the housing of the electric engine with the transmission case. With this type of torque bracing it proves to be advantageous that the oscillations of the power train are transferred only in a damped state to the chassis by the bearing buffers of the internal combustion engine or the transmission. The driving comfort for the passengers is increased, as compared to a mechanical connection of the electric motor to the chassis in order to brace the torque.
In the design of the drive unit, according to certain preferred embodiments of the invention, the points of action of the mechanical connection at the transmission case lie in a horizontal plane. Furthermore, a knuckle joint is provided between the transmission and the electric engine.
In the design of the drive unit, according to certain preferred embodiments of the invention, the points of action of the mechanical connection at the housing of the electric engine lie in a horizontal plane, whereby a knuckle joint is provided between the transmission and the electric engine.
In the design of the drive unit, according to certain preferred embodiments of the invention, the points of action of the mechanical connection at the housing of the electric engine lie in a horizontal plane, where between the transmission and the is electric engine there is a knuckle joint, on both sides of which on a level with its peak a torque bracket is mounted so as to bend.
In the design of the drive unit, according to certain preferred embodiments of the invention, the dead weight of the electric engine is absorbed at least partially by a spring with low damping between the vehicle floor and the housing of the electric engine. Thus, when the power train stutters or splutters, these motions can be absorbed in an advantageous manner.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.